Abstract

Polychlorinated biphenyls (PCB) have been widely applied in industrial processes since the 1930s until the late 1970s. They were first discovered as environmental pollutants in 1966 and prohibited in the early 1980s1. It has been reported that about 640 thousand tonnes of PCB were produced alone in the U.S. between 1929 and 1977. Approximately 25 % was used either in transformers, which functioned submerged in solutions of PCB and polychlorobenzene (PCBz), or in capacitors operated with PCB2. Even in recent years, PCB continue to be detected in water, sediments, soil, as well as tissue of animal species in every part of the world3. Thermal decomposition of PCB is the most widely deployed method to destroy PCB, and a number of earlier studies reported that polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) form during the PCB combustion, fires of electrical equipment and waste incineration of PCB4.5. Due to the environmental toxicity and bioaccumulative nature of PCDD/F, a study on the formation and distribution of PCDD/F in PCB combustion should be helpful to estimate the risk of PCB disposal to the environment, especially in uncontrolled combustion, such as fires. For this study, we selected 4-chlorobiphenyl (4-CB) which has a simple structure that allows us to focus on elucidating the mechanism of its oxidation. To this end, we have carried out a series of laboratory-scale experiments to study the formation of PCDD/F under conditions similar of PCB fires. We also determined the formation of species regarded as precursors for the formation of PCDD/F.